A DNAinfo investigation has found that an astonishing number of Chicago police dash cam videos are lacking audio, including the footage from the October 2014 shooting of 17-year-old Laquan McDonald.

Records suggest that Officer Jason Van Dyke, who has been charged with the murder of McDonald, tampered with his dash cam audio on the day of the shooting, causing “intentional damage” and failing to sync the microphone to the camera.

In the months leading up to the shooting, the dash cam in Van Dyke’s vehicle had to be repaired multiple times. According to police records, on the day of the shooting, it was “apparent…that personnel have failed to sync the MICs.” The footage of the shooting that was released in November was recorded from a different police car that was on the scene.

According to the information obtained by DNAinfo, human error is to blame in 80 percent of the dash cam videos in Chicago that are missing audio. Police officials investigated the phenomenon last month in light of the McDonald video.